Water-in-oil (W/O) emulsions occur at many stages in the production and processing of crude oil. Although varying from case to case, the proportion of water produced from an oil well can make up as much as 90 percent by weight or more of the total production. A portion of the produced water is intimately dispersed as small droplets throughout the oil cut due to naturally occurring surfactants in the crude. In addition, synthetic surfactants can be added to recover residual crude trapped in a reservoir. Also, multiple water-in-oil-in-water emulsions requiring additional separation stages can be encountered during the production in fields with a high water to oil ratio especially when steam is used to mobilize heavy crude oils or bitumens.
In crude oil processing (refining), desalting techniques comprise the deliberate mixing of the incoming crude with a fresh "wash water" to extract the water soluble salts and hydrophilic solids therefrom. However, the presence of water in crude oil can interfere with refining operations, induce corrosion, increase heat capacity and reduce the handling capacity of pipelines and refining equipment.
W/O emulsions are commonly believed to be stabilized by the presence of films formed at oil-water interfaces which prevent coalescence of the dispersed droplets. The interfacial activity of crude oils is thought to result from the presence of polar components including asphaltenes, resins and organic acids. For asphaltenes in particular, the presence of heteroatoms in the essentially aromatic structure impart amphiphilic characteristics.
Both physical and chemical methods have generally been employed, usually in combination, to overcome the barrier presented by the films. Common physical methods include the application of electrical fields, heat and gravitational force to increase the frequency and force of droplet to droplet collisions. Chemical agents typically act on the interfacial film by either reacting chemically with the polar crude oil components or by modifying the environment of the dispersed droplets (demulsification). Among chemical agents, interfacially-active demulsifiers which weaken the stabilizing films to enhance droplet coalescence are preferred due to lower addition rates needed.
The formulation of commercial demulsifiers is largely based on empirical approaches in an effort to obtain increasingly effective and universal materials which can work at smaller dosages with shorter separation times. Typically laboratory testing is followed by evaluation under more representative dynamic conditions in a pilot scale process unit and ultimately in the field. The need for extensive empirical testing is the result of a wide range of factors which affect emulsion stability including emulsification conditions such as temperature and pressure; the nature of the aqueous phase (e. g. salinity and pH); the water-oil ratio; and the composition of the crude oil. Crude oil specificity has long been recognized and many demulsifier products are formulated as a mixture of agents in a carrier solvent to improve performance.
Early demulsification relied on the reversal of the emulsion type demulsifier such as hydrophilic ionic surfactants. These types were followed by oil-compatible, non-ionic surfactants based on ethylene and propylene oxide resins. Recently, chemical demulsifier components include alkoxylated phenolic resin adducts and polyalkylene glycols.
Water-soluble polymeric demulsifiers such as the emulsion tetrapolymer of methylmethacrylate, butyl acrylate, acrylic acid and methacrylic acid in U.S. Pat. No. 5,100,582 and dispersions of water-soluble cationic polymers in U.S. Pat. No. 5,330,650 have also been utilized.
Specific examples of oil-soluble demulsifiers include combinations of polyoxylalkylated alkyl phenol formaldehyde polycondensates with reaction products of diisocyanates and polyoxyalkylated compounds in U.S. Pat. Nos. 3,640,894 and 3,699,051; combinations of oxyalkylated alkyl phenol-aldehyde resins and hydrocarbon polymers in U.S. Pat. No. 4,175,054; alkoxylates in U.S. Pat. No. 5,401,439; the reaction product of diglycidyl groups of an ether with the hydroxyl groups of a polyoxylated alkyl phenol formaldehyde polycondensate in U.S. Pat. No. 3,676,501; polyoxyalkylenes in U.S. Pat. No. 4,183,821; and dicarboxyl acid esters of sulfated oxyalkylated alkyl phenol formaldehyde resins in Canadian Patent No. 774,664. Typically, these oil-soluble demulsifiers are formulated in organic solvents alone such as toluene, xylene, tetrahydrofuran, dioxane, lower alcohols and light gasoline fractions having boiling limits of from 50 to 200.degree. C.; or in co-solvents comprising organic solvents and water wherein the organic solvents are usually C.sub.3 to C.sub.10 alkanols, ethylene diamine, diethylene triamine, or ethanolamines including diethanolamine as exemplified by U.S. Pat. Nos. 4,737,265 and 5,401,439.
Among the disadvantages of having organic solvents in a demulsifier formulation are increased cost, flammability, and toxicity. Therefore, a demulsifier formulation which does not include organic solvents would represent an advance in the art of demulsification.
Demulsification by use of oil-soluble demulsifiers in conjunction with an added excess of water has been disclosed in S.U. 1268185; U.S. Pat. Nos. 5,256,305 and 3,928,194 and JP 03229682. Moreover, combinations of oil-soluble and water-soluble demulsifiers in water have been disclosed in S.U. 1766943. Water-soluble demulsifiers in combination with water-soluble surfactants and oil-soluble surfactants have been disclosed in U.S. Pat. No. 3,756,959. However, these references do not suggest that an stable aqueous formulation of an organic demulsifier or demulsifiers can be made in the presence of water-soluble surfactants.
Accordingly, an object of the present invention is to provide novel, economical and effective processes for resolving emulsions into their component parts of oil and water or brine.
Another object of the present invention is to provide a demulsifier system which breaks the emulsions rapidly and completely at both elevated temperatures and low temperatures and which leaves virtually no residual water and residual salt in the product, and no residual emulsion in the water which is separated off.
It is a further object of the invention to use such demulsifier formulations for carrying out an advantageous process for breaking crude oil emulsions, which process gives crude oils which are free from water and salt, and waste water which is substantially free from emulsion.
Our invention meets such objects by providing an aqueous formulation for oil soluble demulsifiers, made soluble by the addition of surfactants.
Other objects, advantages and features of the invention are described hereinafter.